Method of buffing steel



United States Patent METHOD OF BUFFING STEEL George Albert Lyon, Detroit, Mich.

No Drawing. Application September 3, 1953, Serial No. 378,433

8 Claims. (Cl. 51-281) The instant invention relates to the art of buffing steel, and more particularly, to an improvement in the treatment of wrought stainless steel to smooth-finish the same.

Particularly in the fabrication of stainless steel hub caps, trim rings and the like, where appearance is an essential feature, there has been encountered a great deal of difficulty in perfecting the bufling operation. In the buffing of articles of this nature, there is a very great tendency toward roping and/or orange peel formation. The roping is recognized in the industry as the formation of very fine lines or scratches in the metal surface, presumably because of imperfect cooperation between the bufiing compound and the hard surface of the steel. The orange peel herein referred to is recognized in the industry as another type of imperfection which has the general appearance of the surface of an orange and is possibly caused by the presence of hidden strains in the surface portions of the steel.

The instant invention is based upon the discovery of a particular type of pre-treatment for the steel which uniquely conditions the same for the bufiing operation and greatly facilitates and improves the final buifing operation.

It is, therefore, an important object of the instant invention to provide an improved butting operation for stainless steel.

It is still a further object of the instant invention to provide an improvement in the bufiing of stainless steel which comprises a pre-treating operation for the stainless steel prior to the bufling thereof.

Other objects, features and advantages of the invention will become apparent to those skilled in the art from the following detailed disclosure of preferred embodiments thereof.

The instant invention consists in a method of treating a wrought stainless steel sheet-like article, that comprises immersing the article in a liquid medium maintained at 1200-1300 F. for /2 to 1% minutes, then removing and quenching and finally buffing a surface of the article to smooth-finish the same.

Wrought stainless steels are a well known class of materials including austenitic, martensitic and ferritic steels, 'all of which contain a substantial amount of chromium (at least about 11% and preferably 12-25%). Wrought austenitic stainless steels are characterized by the presence of nickel or manganese and chromium therein in a total amount of at least 23% (and not more than about 50), the Cr content being at least about 14-16% and the Ni and/or Mn content being at least about 7%. Preferred austenitic steels for use in the invention are AlSl type No. 301 (0.08-0.2% C; 16-18% Cr; 6-8% Ni; and max. 2% Mn) and chrome-manganese steel (ODS-0.15% C; 16-18 Mn; and 14-16% Cr). The martensitic steels have 1118% chromium and up to about 1.25-2.5% nickel, an example being AlSl type No. 431 (max. 0.2% C; -17% Cr; and 1.25-2.5% Ni). The ferritic steels have about 11-27% chromium, an example of a particularly preferred steel for use in the "ice invention being AlSl type No. 430 (max. 0.12% C and 14-18% Cr).

Most preferably the steel used is in sheet form (18-22 gauge) and it is formed into sheet-like articles such as hub caps. As an example, a sheet of 18 gauge AlSl type No. 301 wrought stainless steel is drawn (with four applications in a cold-forming operation) to obtain an automobile wheel cover.- There is a protective oil film on this product (since liquid hydrocarbon oils are used in the drawing compounds).-

If this wheel cover is now subjected to a butting operation there is a very great tendency toward roping" and orange pee formation thereon. Removal of the bufiing oil by washing, etc. does not appreciably help this situation. According to the instant invention, this wheel cover is first immersed in a salt bath maintained at a temperature of 1250 F. for one minute. After the wheel cover has been submerged in the bath for one minute it is immediately removed therefrom and quenched. Because of the thinness of the sheet-like article, it may be effectively quenched in the air, but it is quenched in water in the preferred procedure. The wheel cover is then dried and subjected to the normal bufiing operation, which includes the use of bufling compounds containing abrasive No. 300 fines or the like; and it is found that the stainless steel wheel cover buffs very readily and effectively so as to obtain an extremely high degree of smoothness, in the absence of roping or orange peel formation. In fact the stainless steel appears to have a surface film thereon that buffs as easily as copper.

The temperature of the salt bath or similar liquid medium is in the preferred procedure maintained at about 1200-1300 F. and most preferably at 1250 F. The particular salts used are those used in any of the conventional metal treating molten salt baths (and most preferably a eutectic Nacl, KCl and BaClz mix) and need not be herein discussed in further detail. Such baths are usually employed for metal treating purposes such as annealing; but in the instant operation, the bath temperature is maintained clearly below the annealing temperature for the wrought stainless steel (and preferably not less than F. below the annealing temperature). It is, therefore, clear that annealing does not take place to the extent that the properties of the instant wheel cover are wholly changed with respect to resiliency, etc., which are properties that are essential in the proper functioning of the wheel cover. Instead, it appears that some unusual surface phenomenon takes place during this brief period of immersion in the salt bath and the metal in a molecular-like film onthe surface is sufficiently changed to permit the simplified and substantially superior buffing process. Precisely what takes place on the surface of the instant article is not understood; but it hasbeen found that substantially the same results may be obtained using a number of different types of wrought stainless steels. For example, results substantially the same as those just described are obtained using a sheet of 20 gauge AlSl type No. 430 wrought stainless steel (ferritic), and a sheet of 20 gauge chrome-manganese steel (above described).

The time of immersion in the salt bath has been found to be quite significant. For example, if the time is extended to substantially beyond 1% minutes, an excessive amount of oxidation or other corrosion-like reaction appears to take place at the surface and this causes fur ther difficulty instead of simplification during the buffing operation. On the other hand, it is not mechanically possible to submerge the wheel cover and then remove it from the bath in less than at least a few seconds and it has been found desirable to submerge the cover in the bath for at least about A minute. The preferred time is about one minute. I

Although it is not desired to limit the instant invention to any particular theory, it is believed that the presence of the drawing compound (hydrocarbon) oil on the surface of the article may have some important effect in the instant procedure. The procedure is, of course, simplified by omitting the step ofattempting to remove this oil from the article before immersing the same in the bath; but it has been found that the operation leads to superior results if the oil is retained on the article until the article is immersed in the bath. When the article is removed from the bath the surface thereof appears to have a certain amount of black material thereon resembling lampbla'ck (which is believed to be chiefly MnOz plus iron and chrome oxides). This could result from the thermal decomposition of the oil to yield carbon coupled with the inherent oxidizing reactions. Conceivably, there is some surface reaction between the oxidizing atmosphere and/or the carbon and the metal so that the surface film on the stainless steel is advantageously affected. Whatever this effect, it has been found that the overall hardness of the wheel cover is not appreciably affected and the critically important properties such as corrosion resistance, stainlessness, etc. are not affected.

The buffing operation per se is a recognized and established operation in the art involving (as hereinbefore indicated) the use of a bufiing compound which contains abrasive fines. Since this operation is an established operation in the art, it need not be discussed in further detail, except to note that the bufiing operation employed in the practice of the instant invention is greatly simplified and reduced in time spent thereon, because of the excellent bufiing properties of the surface of the instant treated stainless steel.

As another aspect of my invention, it has been found that the buffing operation is still more advantageously simplified if a combined quenching and bufiing compound application is employed. In this operation, the bufiin g compound in admixture with a suitable fusible material such as a salt of the type used in the bath is sprayed or otherwise applied to the surface of the wheel cover, while hot, just after it is removed from the bath. In this manner, the fusion of the salt on the surface of the wheel cover materially assists in the quenching operation and also this fusion results in the adhering of the infusible abrasive grains to the wheel surface. This pre-application" of the buffing compound further simplifies the buffing operation and improves the same in that it effects a uniform initial application of the buffing compound to the surface of the wheel cover; in fact, it is believed that the subsequently hardened salt itself assists in the initial phases of the buffing operation.

It will be understood that modifications and variations may be effected without departing from the scope of the novel concepts of the present invention.

I claim as my invention:

1. A method of treating a wrought stainless steel sheet-like article, that comprises immersing the article in a liquid medium maintained at 1200-l300 F. for

/2 to 1 /2 minutes, then removing and quenching and finally buffing a surface of the article to smooth-finish the same.

2. A method of treating a Wrought stainless steel sheet-like article that is cold-formed, that comprises immersing the article in a liquid medium maintained at 1250 F. for one minute then removing and quenching and finally bufiing a surface of the article to smooth-finish the same.

3. A method of treating a wrought stainless steel sheet like article that is cold formed and has an oil film thereon, that comprises immersing the article in a liquid molten salt medium maintained at 1200-1300 F. for one minute then removing and quenching and finally bufling a surface of the article to smooth-finish the same.

4. A method of treating a wrought stainless steel sheet, that comprises cold-forming the sheet into the shape of an article, immersing the article in a liquid medium maintained at 1200-1300" F. for /2 to 1V2 minutes, then removing and quenching and finally buffing a surface of the article to smooth-finish the same.

5. A method of treating a wrought stainless steel sheet. that comprises applying a protective oil film to the sheet and cold-forming the sheet into the shape of an article, immersing the article in a liquid medium maintained at 12001300 F. for /2 to 1 /2 minutes, then removing and quenching and finally buffing a surface of the article to smooth-finish the same.

6. A method of treating a wrought stainless steel sheet-like article, that comprises immersing the article in a liquid medium maintained at 1200-1300 F. for A. to 1 /2 minutes, then removing and applying buffing compound to the article while cooling to cause the compound to fuse and adhere to the article, and finally buffing a surface of the article to smooth-finish the same.

7. A method of treating a wrought stainless steel sheetlike article, that comprises immersing the article in a liquid medium maintained at 1200l300 F. for /2 to 1% minutes, then removing and spraying the article with buffing compound containing fusible salt to fuse and adhere the compound to the article, and finally buffing a surface of the article to smooth-finish the same.

8. A method of treating a wrought stainless steel sheet-like article, that comprises immersing the article in a liquid medium maintained at at least 1200 F. and not less than F. below the steel annealing temperature for one minute, then removing and quenching and finally buffing a surface of the article to smooth-finish the same.

References Cited in the file of this patent UNITED STATES PATENTS 1,686,223 Armstrong Oct. 2, 1928 1,977,448 Lyon Oct. 16, 1934 2,332,992 Davis Oct. 26, 1943 2,471,727 Creamer May 31, 1949 

1. A METHOD OF TREATING A WROUGHT STAINLESS STEEL SHEET-LIKE ARTICLE, THAT COMPRISES IMMERSING THE ARTICLE IN A LIQUID MEDIUM MAINTAINED AT 1200-1300* F. FOR 1/2 TO 11/2 MINUTES, THEN REMOVING AND QUENCHING AND FINALLY BUFFING A SURFACE OF THE ARTICLE TO SMOOTH-FINISH THE SAME. 